1. Field of the Invention
The present application relates generally to static fluid mixers and particularly to static mixers which are useful in generating fluid mixing vortices. The application also relates to methods for mixing fluids using such static mixers.
2. The State of the Prior Art
Static mixers positioned within pipes or other conduits are used in a variety of applications to facilitate mixing of one or more fluid streams flowing within the conduits. For example, static mixers are used to cause a homogeneous distribution of a gas or solid particles within a liquid stream, for mixing of two or more gas or liquid streams, and for mixing a single fluid stream to cause a more uniform distribution of temperature, velocity or other fluid properties.
Certain types of static mixers, known as vortex mixers, are specifically designed to cause mixing by creating swirling vortices of fluid. Examples of such vortex mixers are shown in U.S. Pat. No. 4,307,697 to Ong, U.S. Pat. No. 5,330,267 to Tauscher, U.S. Pat. No. 6,456,533 to Streiff et al., U.S. Pat. Nos. 4,929,088 and 4,981,368 to Smith, U.S. Pat. No. 5,489,153, and U.S. Pat. No. 5,813,762, each of which are incorporated herein by reference.
It is generally desirable for a vortex mixer to provide both a short mixing flow path and a small pressure loss under a variety of different flow conditions and fluid compositions. In addition to achieving high efficiency, it is also desirable for the vortex mixer to be of simple, yet durable, construction for ease of fabrication and reduced cost. The above-referenced vortex mixers meet these objectives to varying degrees; however, the need for an improved vortex mixer continues.
It is an object of the invention to provide a static mixer that is capable of providing high mixing efficiency across a range of different fluid flow rates so that the mixer may be used in a variety of different applications.
It is also an object of this invention to provide a static mixer that provides high mixing efficiency for two or more substances, such as gas and liquid streams or solid particles and fluid streams, flowing within a conduit across a wide range of ratios of one substance to the other(s) so that the mixer is useful in many different applications.
It is another object of this invention to provide a static mixer that achieves a high degree of mixing while causing only a relatively low pressure drop so that energy losses can be maintained within preselected limits.
It is yet another object of this invention to provide a static mixer that is constructed to impede the collection of fibers or other solid particles on surfaces of the mixer so that the opportunity for clogging of the conduit is minimized when fluids containing fibers or solid particles are flowing through the conduit.
It is a further object of this invention to provide a static mixer that is of a simple configuration and which is made from a minimum amount of material so that low fabrication and manufacturing costs can be obtained.
As a corollary to the preceding object, it is a still further object to provide a static mixer that has a strong and stable construction so that it able to resist vibrations and fluid forces with minimal risk of failure.
To achieve these and other related objects of the invention, a static mixer is provided which, in the preferred embodiment, uses only two baffle members positioned within a preselected length of conduit, one baffle member being positioned downstream from and at approximately a 90 degree offset from the other baffle member. Each baffle member is constructed in a manner to create a pair of counter-rotating vortices that are able to spread across the entire cross section of the conduit. Because of the offset baffle members, the static member produces mixing distribution in two main directions across the cross section of fluid flow, further contributing to homogeneous mixing along a relatively short length of conduit and with a minimum of pressure drop.
Specifically in one broad aspect, the invention provides a static fluid mixer that comprises an elongated fluid flow conduit having a centrally located longitudinally extending axis and an inner generally cylindrical wall extending around said axis and defining a fluid flow path within the conduit which extends along said central axis. Also the mixer includes a first elongated inclined baffle member positioned in said fluid flow path at a first location in said conduit and a second elongated inclined baffle member positioned in said fluid flow path at a second location in said conduit. The second location is offset circumferentially from the first location and the same is spaced longitudinally of the conduit from said first location. The arrangement of the baffle members is such that the mixer includes no additional baffle members which are aligned either circumferentially or longitudinally with either the first baffle member or the second baffle member.
In another broad aspect, the invention provides a static fluid mixer comprising an elongated fluid flow conduit having a centrally located longitudinally extending axis and an inner generally cylindrical wall extending around said axis and defining a fluid flow path within the conduit which extends along said central axis. The mixer includes a first elongated inclined baffle member positioned in said fluid flow path at a first location in said conduit. The first baffle member is in the form of a plate having an upstream end, a downstream end and a longitudinal axis. The upstream end of the first baffle member is spaced radially from the wall a first distance which is less than a radius of the conduit, and the downstream end of the first baffle member is spaced radially from the conduit a second distance which is greater than said first distance.
The mixer further includes a second elongated inclined baffle member positioned in said fluid flow path at a second location in said conduit. The second baffle member also is preferably in the form of a plate having an upstream end, a downstream end and a longitudinal axis. The upstream end of the second baffle member is spaced radially from the wall a third distance which is less than the radius of the conduit and the downstream end of the first baffle member is spaced radially from the wall a fourth distance which is greater than said third distance. Preferably the second and fourth distances are such that the baffle members span approximately 70 percent of the diameter of the conduit. It is also preferred that the first and third distances comprise approximately 4 percent of the diameter of the conduit. The second location in the conduit is preferably offset circumferentially from the first location and spaced longitudinally of the conduit a fifth distance from said first location.
The mixer may also include a mounting element for each of said baffle members. Preferably these mounting elements may extend radially of the conduit between a downstream face of a respective baffle and said wall. Ideally, the mounting elements may each be in the form of a member having an edge which contacts the wall of the conduit along a line which is essentially parallel with the central axis. Alternatively at least one of the mounting elements may be in the form of a sparger pipe.
In a preferred form of the invention, the baffle members are of essentially the same shape, the first and third distances are essentially the same, and the second and fourth distances are essentially the same. Ideally, the members may be plates which are trapezoidal in shape. Ideally, the first and third distances are sufficiently large to permit portions of the fluid flowing through the conduit to pass between the upstream ends of the baffle members and the wall.
In yet another preferred aspect of the invention, the downstream ends of the baffle plate members may have laterally spaced corners which are arranged to create counter-rotating vortices in the fluid flowing through the conduit. This arrangement facilitates thorough mixing of the materials flowing through the conduit.
In another preferred form of the invention, the longitudinal distance between the first and second locations where the baffle members are positioned should be in the range of from approximately 2 times to approximately 10 times greater than the radius of the conduit. Ideally, such longitudinal distance may be approximately 4 times larger than said radius.
Preferably, the baffle members may be offset circumferentially approximately 90xc2x0 apart. In addition, in accordance with another preferred aspect of the invention, a longitudinal axis of each of the baffle members may be inclined at an angle in the range of from about 20 to about 60 degrees relative to the central axis of the conduit. Even more preferably, the longitudinal axes of the baffle members may be inclined at an angle in the range of from about 30 to about 50 degrees relative to the central axis of the conduit. Ideally, the longitudinal axes of the baffle members may each be inclined at an angle of about 35 degrees relative to the central axis of the conduit. In accordance with another preferred aspect of the invention, the upstream ends of the baffle members may be inclined at an angle of about 90 degrees relative to said axis.
The baffle members may ideally be plates which are trapezoidal in shape with downstream ends which are smaller than the upstream ends. In accordance with the principles and concepts of the invention, the baffle plates may have any one of a variety of shapes and configurations. That is to say, the members may be plates which are essentially planar in traverse cross-sectional configuration. Alternatively, the members may be essentially non-planar in traverse cross-sectional configuration, essentially concave in traverse cross-sectional configuration, essentially convex in traverse cross-sectional configuration, or essentially V-shaped in traverse cross-sectional configuration. The baffle members may also include a hollow internal or external passageway providing a flow path for introducing an additive into a flow of fluids passing through the conduit. Alternatively, the baffle members may be in the form of porous and/or foraminous plates.
The invention further provides a method of mixing one or more fluid streams comprising providing a static fluid mixer as described above and causing one or more fluid streams to flow along the fluid flow path defined by the conduit. The invention also provides a method of mixing solid particles with one or more fluid streams comprising providing a static fluid mixer as described above and causing a stream of solid particles and one or more fluid streams to flow along the fluid flow path defined by the conduit.